Synthetic polymers have been successfully employed for setting hairstyles for almost 50 years. Initially, homopolymers and copolymers of vinyllactam were preferably employed; later on, polymers containing carboxylate groups became increasingly important. The desired set of properties, such as high strength under conditions of high atmospheric humidity, elasticity, ease of washoff from the hair, and compatibility with the other formulating components, is obtained by copolymerizing a combination of hydrophobic, elasticizing and carboxyl-containing monomers (reference: Robert Y. Lochhead, Vol. 103, December 1988, 24 ff., Rolf-Dieter Reinhardt Cosmetics and Toiletries Manufacture World Wide 1995, 189m ff.).
Although the requirements set out above are nowadays attained by various types of polymer, the handle of hairstyles set using these polymers is being perceived more and more frequently as unpleasantly dull and "not natural". Attempts to obtain an improvement by making additions to the formulations have so far led to results which are not entirely satisfactory: The addition of customary plasticizers, although improving the handle, in many cases reduces the setting effect at the same time. The polysiloxanes frequently employed are incompatible with the polar polymers and in many cases require further additives if they are to be formulated at all. Instances of separation can lead to problems both during storage of the formulation and during its use (cf. EP-A 0 408 311, p.1, line 25 et seq.).
There has therefore been no lack of attempts to bond polysiloxane groups covalently to the hairsetting polymer in order to prevent instances of separation. EP-A-0 408 311, for example, describes haircare polymers comprising a monomer which contains polysiloxane groups, together with the customary hydrophilic and hydrophobic monomers. EP-A-0 412 704 to 707 propose polymerizing polysiloxane groups, in the form of macromonomers having molar masses from 1000 to 50,000, likewise with hydrophobic and hydrophilic monomers.
The synthesis of macromonomers containing siloxane groups is extremely laborious. Because of their high molecular weight, it is virtually impossible to separate unreacted macromonomers and their unreactive impurities from the polymers. They constitute a toxicological and allergenic risk and impair the solubility. Furthermore, to obtain a good effect, the resulting copolymers can often be formulated only in combination with other polymers, carriers and further auxiliaries, as taught by the abovementioned patent documents.